Spectral sensitization of silver halide photographic emulsions is an extremely important and indispensable technique for preparing photographic light-sensitive materials which have a high sensitivity and which are excellent in color reproducibility. For the purpose of providing photographic light-sensitive materials having a high sensitivity, various spectral sensitizers have heretofore been developed and additionally, the technical development of the use of spectral sensitizers, for example, for super color sensitization with spectral sensitizers or for advantageous addition of spectral sensitizers has also been performed. A spectral sensitizer can absorb even light with a long wavelength range, which inherently is not substantially absorbed by silver halide photographic emulsions, and has an action of transmitting the light absorption electron and/or the light absorption energy to silver halides. Accordingly, the increase of the amount of the light trapped by the spectral sensitizer may be advantageous for elevating the photographic sensitivity of photographic emulsions. Under the situation, not only a trial of developing spectral sensitizers having an elevated light absorption coefficient but also a trial of increasing the amount of the spectral sensitizer to be added to silver halide emulsions to thereby elevate the amount of the light to be trapped by the spectral sensitizer have been performed.
Accordingly, improvement and development of means of increasing the amount of spectral sensitizers to be added to silver halide emulsions as well as improvement and development of preparation of such silver halide grains capable of accepting an increased amount of spectral sensitizers have variously been tried up to the present.
For example, Thomas L. Penner & P. B. Gilman Jr., Photographic Science and Engineering, 20 (3), 97-106 (1976) has proposed a means of stratiform-absorbing a large amount of two different spectral sensitizers which are in a pertinent potential relation to silver halide crystals to thereby increase the amount of light to be trapped by the spectral sensitizers while the desensitization caused by the large addition of the spectral sensitizers is suppressed. In addition, a trial of improving the silver halides themselves has also been performed. One improvement is to use tabular silver halide grains having a large specific surface area, which is disclosed in Japanese patent application (OPI) Nos. 113926/83, 113927/83, 113930/83, 113934/83, 111934/83, 95337/83, 108528/83, 108526/83, etc. (The term "OPI" as used herein means a "published unexamined patent application".)
On the other hand, C. R. Berry & D. C. Skillman, J. Appl. Phys., 35, 2165-2169 (1964) and J. E. Maskasky's Japanese patent application (OPI) No. 133540/84 mention silver bromide grains having silver chloride epitaxially grown on the surface of the base grain.
Although the examples of these grains are not naturally intended to increase the specific surface are of the grains, this is one method of increasing the specific surface area of silver halide grains.
However, all of these grains could not be expected to sufficiently increase the specific surface area of the grains as compared with grains having the same size but having no protrusions, since the size of the protrusions epitaxially grown on the surface of the base grains is too large and/or the number of the protrusions per unit area is too small.
Small protrusion are advantageous with respect to the enlargement of the specific surface area. Accordingly, a means of first forming smaller protrusions on the surface of base grains and then stabilizing the resulting grains in the subsequent process, especially during chemical sensitization of the grains, has been tried, and for example, Japanese patent application No. 300410/86 (corresponding to U.S. patent application Ser. No. 133,974 filed on December 17, 1987) discloses a method for stabilizing the grains with a grain formation-stopping agent prior to the chemical sensitization of the grains.
However, the addition of the grain formation-stopping agent before chemical sensitization resulted in a noticeable limitation in the successive process (especially in the chemical sensitization step).
For example, when the variation of the shape of the grains is stopped by the addition of a mercapto compound (especially, 1-phenyl-5-mercaptotetrazole) prior to chemical sensitization of the grains, the chemical sensitization would be extremely retarded or fog would often increase. Moreover, the subsequent spectral sensitization step would also become disadvantageous, as the adsorption of dyes would be inhibited or formation of association products would be inhibited.
Therefore, Japanese patent application No. 300410/86 mentions that a dye having both a grain formation-stopping function and a spectrally sensitizing function is preferably used so as not to impart any adverse influence to the spectral sensitization step.
However, the optimal dye capable of acting as a grain formation-stopping agent does not always correspond to the optimal dye capable of acting as a spectral sensitizer, and therefore, in most cases the degree of freedom for the selection of the dyes for spectral sensitization is reduced or the photographic characteristics such as color-sensitivity, etc., are sacrificed.
Moreover, since a large amount of the grain formation-stopping agent is added, a large amount of an organic solvent would thereby have to be used in most cases, and as a result, the handling of the subsequent process would often be extremely difficult, particularly when the operation of rinsing with water is successively required.